Activity of Zn and Mg phthalocyanines and porphyrazines in amyloid aggregation of insulin

Abstract

Formation of the deposits of protein aggregates—amyloid fibrils in an intracellular and intercellular space—is common to a large group of amyloid‐associated disorders. Among the approaches to develop of therapy of such disorders is the use of agents preventing protein fibrillization. Polyaromatic complexes—porphyrins and phthalocyanines—are known as compounds possessing anti‐fibrillogenic activity.Here, we explore the impact of related macrocyclic complexes—phthalocyanines (Pc) and octaphenyl porphyrazines (Pz) of Mg and Zn—on aggregation of amyloidogenic protein insulin. Pz complexes are firstly reported as compounds able to affect protein fibrillization.The effect of Pc and Pz complexes on the kinetics and intensity of insulin aggregation was studied by the fluorescent assay using amyloid sensitive cyanine dye. This has shown the impact of metal ion on the anti‐fibrillogenic properties of macrocyclic complexes—the effect on the fibrillization kinetics of Mg‐containing compounds is much more pronounced comparing to that of Zn analogues.Scanning electron microscopy experiments have demonstrated that filamentous fibrils are the main product of aggregation both for free insulin and in the presence of macrocyclic complexes. However, those fibrils are distinct by their length and proneness to lateral aggregation. The Pc complexes cause the increase in variation of fibrils length 0.9 to 2.7 nm in opposite to 1.4 to 2.0 nm for free insulin, whereas Pz complexes cause certain shortening of the fibrils to 0.8 to 1.6 nm.The averaged size of the fibrils population was estimated by dynamic light scattering; it correlates with the size of single fibrils detected by scanning electron microscopy.

Study of tetraphenylporphyrins as modifiers of insulin amyloid aggregation

“…Previously, we have demonstrated the influence of the central metal atom (Mg or Zn) in porphyrazines and phthalocyanines on the efficiency of insulin fibrillization inhibition by these compounds, which was explained by the ability of Zn ion to coordinate histidine and cysteine amino acid residues in proteins . Thus, we could suppose that Pd does not affect the inhibitory properties of tetraphenylporphyrin due to the inability of this metal atom to form additional coordination bonds.…”

“…There are two amyloidogenic sequences in the structure of insulin, which are critical for amyloid aggregation; these are (11)LVEALYL(17) or its versions (11)LVEALY(16) and (12)VEALYL(17) located in the B chain and (13)LYQLEN(18) located in the A chain . The inhibition of the protein fibril formation by macrocyclic aromatic compounds (such as porphyrins) is known to be mainly based on the π‐π stacking of the porphyrin chromophore and aromatic amino acid residues of the protein; in the case of insulin, these residues possibly are the tyrosine (Y) ones of the amyloidogenic sequences …”

“…Particularly, the heme‐like complexes such as porphyrins and phthalocyanines are widely studied as compounds that can influence the process of fibril formation . For planar phthalocyanines and porphyrazines with “opened” (i.e., without out‐of‐plane coordinated ligands) central metal atom, it was shown that this central atom contributes to the compound's interaction with protein, thus affecting the degree of protein aggregation inhibition and the morphology of the formed aggregates . We have previously discovered the antifibrillogenic activity of the axially coordinated phthalocyanines .…”

Self‐Assembled Porphyrazine Nucleosides on DNA Templates: Highly Fluorescent Chromophore Arrays and Sizing Forensic Tandem Repeat Sequences

“…Inspired by these reports, we explored the use of a zinc porphyrin 2′‐deoxyuridine building block (ZnTPP‐dU 1 , Figure ) which serves us well for covalent DNA modification . In addition to the porphyrin, we also studied a new derivative based on magnesium(II) 5,10,15,20‐tetraaza porphine (porphyrazine, MgTAP‐dU 2 ); TAP (and the related phthalocyanines) derivatives are promising molecules for use in photovoltaics, theranostics, photodynamic therapy, or as anti‐fibrillogenic agents . Both nucleosides 1 and 2 were tested for their ability to form stable non‐covalent arrays against adenosine containing ODN templates by virtue of natural base‐pairing, and their optical properties were analyzed using UV/Vis and fluorescence spectroscopy.…”

Modification of insulin amyloid aggregation by Zr phthalocyanines functionalized with dehydroacetic acid derivatives

“…Many external factors can strongly affect the stability of fibrils and the final structure of amyloid aggregates [36]. We have previously reported that the presence of macrocyclic metal complexes, namely out-of-plane coordinated phthalocyanines [37][38][39], planar phthalocyanines and porphyrazines [40] and tetraphenylporphyrins [41], are able to inhibit the fibril formation or significantly change the morphology of formed protein aggregates. Particularly, the presence of out-of-plane coordinated phthalocyanines led to the formation of different aggregate populations (small amount of protofilaments, oligomeric or unstructured amorphous aggregates) depending on the structure of their out-of-plane ligands [37][38][39].…”